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 Topic: Geophysics Subject: scpt
 Author: fernando bonito 2002-04-30 i would like to know about the limitations, in terms of deph, for scpt (source=hammer +plank). better; what is the critical deph for the geophone to receive a good signal? maybe it depends on the estratigraphy,but would to hear your comments......regards Reply to this posting
Follow-up:
 Author: Paul Mayne 2002-05-01 Hi Fernando,In general, you can reach depths of 30 to 40 meters, althoughin special setups, as deep as 80 to 100 m. Most penetrometersare electric and require amplification of signals up at thesurface when read by the computer. Some penetrometers areelectronic and have the signal conditioning & amplificationdownhole. Thus, you not need to whack the source so much.We use an electric solenoid-source but only for depths of 10m (with electronic Hogentogler cones). We built a pneumaticimpulse source, good to say 20 m. When we go to 30 and 40 m depths, unfortunately we're back to the old pendulum (sledgehammer swinging on a steel frame). Vertek has built a specialhydraulic impulse source that is large and mounted on base of large 30-tonne cone truck. This can reach 60 m depths and costs on order of US \$20k.Regards,Paul

Follow-up:
 Author: Bill Schwartz 2002-07-21 Hello FernandoI agree with Paul's comments, although 80 to 100 meters for a max depth is optimistic.As Paul stated, the determining factor regarding the depth you achieve is your "source". I have found that a steel beam, placed under the jacks of the drill is usually suitable to depths of 30 to 40 meters. Ensuring the beam is level and coupled to the ground surface with the drills weight will produce better results.In addition to the wave source generators that Paul mentioned you might want to try using a "Buffalo Gun".This wave source simply fires a 12 gauge shot gun shell into the ground and produces a higher energy wave. I am not sure if a specific company makes a buffalo gun as the ones I have seen were home made. ( A welder, some scrap steel and some shotgun shells....voila! Buffalo Gun)Note: If you have a surficial layer of peat you might have problems get deep s-wave data as peat tends to dampen your signal.Hope this helpsBill Schwartz